| Summary: | We herein present a weakly-coupled double bow-tie multi-ring elliptical core multi-mode fiber (DBT-MREC-MMF) supporting 22 eigenmodes for mode division multiplexing across the C+L+U band. The proposed fiber introduces a multi-ring elliptical core, bow-tie air holes, and bow-tie stress-applying areas to effectively split adjacent eigenmodes. By utilizing the finite element method (FEM), we accordingly optimized the fiber to support the 22 modes under the weakly-coupled condition. We evaluated the impact of fiber parameters on the minimum effective refractive index difference (min Δ<i>n</i><sub>eff</sub>) between adjacent eigenmodes, model birefringence (<i>B</i><sub>m</sub>), and bending loss at a wavelength of 1550 nm. Additionally, broadband performance metrics, such as effective modal index (<i>n</i><sub>eff</sub>), effective index difference (Δ<i>n</i><sub>eff</sub>), effective mode area (<i>A</i><sub>eff</sub>), differential mode delay (DMD), and chromatic dispersion (D), were comprehensively studied over the entire C+L+U band, ranging from 1530 to 1675 nm. The proposed fiber is capable of supporting 22 completely separated eigenmodes with a min Δ<i>n</i><sub>eff</sub> between adjacent eigenmodes larger than 3.089 × 10<sup>−4</sup> over the entire C+L+U band. The proposed DBT-MREC-MMF holds great potential for use in short-haul communication systems that require MDM to improve transmission capacity and expand bandwidth.
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